


Cryptography

by copacet



Category: Firefly
Genre: Family, Gen, Pre-Series
Language: English
Status: Completed
Published: 2017-06-04
Updated: 2017-06-04
Packaged: 2018-11-04 20:59:48
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,331
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10998885
Author URL: https://archiveofourown.org/users/copacet/pseuds/copacet
Summary: When River is six, she writes her brother an encrypted message.





	Cryptography

**Author's Note:**

  * For [Karmageddon](https://archiveofourown.org/users/Karmageddon/gifts).



The Morrisons are having their annual ball tomorrow night. It promises to be as boring as usual, since Simon is likely to be the only teenager there, but at least River is finally old enough to be invited, so he’ll have _someone_ to talk to. Still, the event means that Simon has to dress nicely, which means his mom is making him lay out his clothes a day in advance, which means he has to figure out where he could have possibly mislaid his tie in the weeks since he last went to one of his parents’ friend’s parties.

It was a nice tie, too, one his dad had gotten him for his birthday. He could wear one of his older ties, of course—his parents have drilled into him from an early age the importance of a neat appearance, so he has several—but he doesn’t want the lecture when his father inevitably asks where the new one went. He closes his closet, casts his gaze around the room to see if it’s lying somewhere out in the open, then, in a fit of desperation, checks his underwear drawer. No luck.

He turns take another look around the room, then stops. Standing just outside the door, her head poking around the frame, is his younger sister. She catches his gaze and grins at him, slipping into the room.

“Not now, River,” he tells her.

She ignores him, holding out one hand with a piece of paper clutched in her fist. “I have an important message for you.”

Sighing, he takes it, holding it up to the light.

It reads: EUAX ZOK NGY HKKT YKOFKJ LUX ZNK CGX KLLUXZ. ZNK GRROGTIK ZNGTQY EUA LUX EUAX IUTZXOHAZOUT.

Simon raises an eyebrow. “Mei-mei, is this some kind of...code?”

“It’s not a _code_ ,” River tells him, crossing her arms. “It’s a cipher.”

“Aren’t they the same thing?” Simon asks, though if River is making a distinction, then he already knows that they aren’t.

River cocks her head. “A code is a method of encryption that operates at the level of semantics,” she tells him, in the tone of one explaining something very obvious. “It’s not a code unless entire words or phrases are being substituted.”

Simon looks again at the jumbled string of letters, interested despite himself. “And a cipher?”

“A cipher operates at the level of syntax. Individual letters are systematically transformed.” She taps the paper. “You have to figure out the system to determine the original meaning.”

“I see.” He squints at the paper again before turning back to his sister. “And remind me why you couldn’t just write down the original meaning?”

“In case the message gets _intercepted_ , Simon.” Her voice drops to a whisper, eyes widening. “Independent spies could be monitoring our every communication.”

“Right,” Simon says. “Of course.” Well, this does seem like a more fun way to spend his evening than hunting through his closet. And he’s not too old to play Alliance and Independents if he’s doing it with his six-year-old sister.   

Also, there’s no way he’s going to be defeated by a code—that is, a _cipher_ _—_ written by said six-year-old sister, no matter how much of a genius she is. He’s going to figure it out to prove that he can, if nothing else.   

“All right,” he tells her.

River grins up at him, then spins on her heel. “Tell me when you figure it out!” she calls as she dances out the door.

“Don’t go too far, ‘cause it won’t be long!” he shouts after her, but she’s already gone.

Simon spends the rest of his evening researching ciphers on the Cortex, applying each one he finds to the sequence of letters his sister has given him. Eventually, he finds the right one: an ancient code named after a long-dead general from Earth-That-Was. It’s a simple substitution cipher; each letter offset the same number of positions down the alphabet. It takes Simon six tries to guess the correct offset, but when he does, the jumble transforms into English.

It now reads: YOUR TIE HAS BEEN SEIZED FOR THE WAR EFFORT. THE ALLIANCE THANKS YOU FOR YOUR CONTRIBUTION.

_“River!”_

No sooner has he shouted than a giggle comes from the direction of his door. He snaps his head around to where his sister is once again poking her head around the doorway; she giggles again, pulling the strip of fabric out from behind her back and waving it in front of her face. He lunges for it, but she’s already taking off down the hallway. “River, give it back!” he calls.

Simon chases her down the hall and then down the stairs. He starts to catch up with her as they run through the living room—he may not be smarter than his little sister, but at least he’s still taller—and River looks over her shoulder at him as she rounds the corner, shrieking with laughter.

River’s mirth cuts off abruptly as she runs straight into their mother, standing just outside of her home office, and falls to the ground. Simon skids to a halt, narrowly avoiding the same fate.

His mom bends over to check on River, who waves her away, then looks back at Simon. “And what exactly are the two of you doing, may I ask?”

Simon takes in the scene before him: River sprawled dramatically on the floor, his mom standing over both of them with her hands on her hips. He clears his throat, clasping his hands behind his back in the hopes of looking dignified. “We were just getting ready for the Morrisons’ tomorrow,” he tells her.

His mom raises her eyebrows, the corner of her mouth quirking upward. “I see. Could you possibly be persuaded to get ready _without_ any mayhem?”

“Yes, mom,” Simon says obediently. River, sitting up, echoes his words.

After their mom leaves, Simon walks over and reaches out a hand to pull River to her feet. He grabs the tie still held in her fist as he does so, and mutters, “ _Brat_ ,” under his breath, but he’s smiling.

* * *

 When River is eight years old, she goes away to a mathematics camp for the summer. A week after she leaves, the first letter arrives. It’s a story about a girl, the main character from a holomovie the family had watched together a few months before. In the movie, the young woman had traveled to the outer planets in search of her missing lover; in the tale that River has written, she lands on a newly-colonized moon and is rewarded with a lavish feast after rescuing a group of villagers from an indigenous animal.

It’s an odd story. Not badly written—River is as gifted at this as she is at everything else—but Simon’s not quite sure why she’s suddenly decided to venture into fiction, or why certain words are underlined, seemingly at random. And then there’s the logistical question of how an isolated colony in the Rim would get the food for the feast in the first place—it’s a minor inconsistency, but River doesn’t _do_ inconsistencies.

Finally it hits him: this is a code. An actual code, this time; not a cipher. He reads the letter again, more carefully. If the heroine is supposed to be River, then the moon must be the camp. Then the town sheriff would be...Simon himself? No, the sheriff is their dad, which makes the mayor of the colony their mom, which makes the reward given to the heroine—?

Finally, he figures it out. Snorting to himself, Simon gets up and heads toward the kitchen. “Hey mom,” he calls. “River wants you to send her some of your homemade cookies!”

* * *

 When River is fourteen, she leaves for the best academic program that money can buy, a bounce in her step and a laugh in her voice as she calls goodbye to Simon while walking out the door. Three weeks later, he gets the first letter.


End file.
